Montana Moss Agate

Physical Properties

Hardness: 6.5-7 (Mohs), Color: Translucent grey-blue to white with black/brown dendritic patterns, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline (Trigonal), Specific Gravity: 2.58-2.64

Formation & Geological History

Formed in the Yellowstone River Basin during the Cenozoic era. Silica-rich water filled cavities in volcanic rock, and minerals like manganese and iron seeped in before the silica solidified, creating tree-like or spotty patterns.

Uses & Applications

Primarily used in jewelry making, cabochons, and as a semi-precious collector gemstone. Known for its durability and unique landscape-like patterns.

Geological Facts

Specifically found in the alluvial gravels of the Yellowstone River. It is the state gemstone of Montana and is highly prized for its 'scenes' that look like moss, trees, or mountains.

Field Identification & Locations

Identify by its translucent greyish base and distinct, dark branching inclusions. Found in riverbeds and gravel bars across eastern Montana. Highly sought by lapidaries.

Identified on: 5/2/2026

Mode: Standard